fix glfwWindow for os x

+ include Cocoa headers if OS X
+ switch filetype in XCode to 'Objective-CPP'
+ fix hanging curly bracket related to os x  #ifdef

Signed-off-by: tgfrerer <tim@poniesandlight.co.uk>
Merge pull request #13 from tgfrerer/feature-elinuxProgrammableGL

fix glfwWindow for os x